U.S. Pat. No. 4,459,073 assigned to the assignee of the predecessor in interest of this application discloses an early embodiment of a self-piercing and riveting fastener of the general type disclosed herein and method of installing the male fastener in a panel. As shown in this patent, the male fastener includes a threaded shank portion, a radial flange portion integral with the shank portion and a tubular barrel portion integral with the flange portion and coaxially aligned with the shank portion. The male fastener is installed in a panel by supporting the panel on a die member or “die button” and driving the distal end of the barrel portion against the panel, piercing a slug from the panel and the deforming the distal end of the tubular barrel portion radially outwardly and deforming the panel surrounding the pierced panel opening between the radial flange portion and the L-shape barrel portion. This embodiment of the self-piercing male fastener and method of installation in a panel was not commercially successful because the fastener and panel assembly had insufficient integrity, including pull-out strength and no means was provided to prevent rotation of the stud in the panel. U.S. Pat. Nos. 4,915,558 and 5,092,724, also assigned to the assignee of the predecessor in interest of the assignee of this application, discloses a commercially successful self-piercing male fastener and method of installation, wherein the fastener includes a shank portion, a radial flange portion and a tubular barrel portion as described above; however, the tubular barrel portion has an axial length generally equal to the outer diameter of the barrel portion and the male fastener is installed in a die member having a concave die surface, including a frustoconical opening and a concave annular bottom surface joining the frustoconical surface by an annular radial lip. The distal end of the tubular barrel portion is driven against a panel supported on the die member, which pierces a slug from the panel, and the distal end portion of the tubular barrel portion is deformed in the concave annular guide surface into a U-shape, wherein the panel surrounding the pierce panel opening is driven inwardly by the annular radial lip of the die member into the U-shaped barrel portion, tightly packing the panel between the radial flange portion and the U-shaped barrel portion. Although this male fastener and method of installation has been commercially successful, the male fastener and method of assembly is not suitable for high performance applications, such as automotive seat belt retaining studs, wherein the male fastener element must be formed of a high strength steel, or in applications having a panel thickness of greater than about 2 mm. It has been found that the barrel portion will crack when deformed into a U-shape as disclosed in U.S. Pat. No. 4,915,558, resulting in poor male fastener and panel assembly integrity.
High performance applications of this type of fastener also requires improved torque resistance. U.S. Pat. No. 6,122,816, assigned to the assignee of this application, discloses a male fastening element of the type disclosed herein, wherein the outer surface of the barrel portion is frustoconical and the radial flange portion includes an outer surface having a plurality of circumferentially arcuate radially inwardly concave surfaces, improving torque resistance when installed in a panel. In the method of installation disclosed in this patent, the radial flange portion is driven into the panel and the panel is then deformed into the arcuate radially inwardly concave surfaces providing torque resistance. Reference is also made to copending U.S. application Ser. No. 10/271,480 filed Oct. 16, 2002, assigned to the assignee of this application, which discloses a male fastening element of the type disclosed herein, wherein the outer surface of the radial flange portion includes a plurality of circumferiantially spaced radially projections or teeth which are driven into the panel during installation and provide greater torque resistance.
However, there remains a need for a self-riveting male fastener or stud of the type described above specifically for high performance applications, wherein the stud is formed of a high strength steel suitable for such applications. The self-riveting male fastener and method of installation of this invention is particularly suitable for high performance applications, wherein the stud is formed of a high strength steel which avoids cracking of the barrel during installation and may be installed in thicker metal panels as required for safety related applications.